The present invention relates to an apparatus and method for performing tests on a sample of body fluid to be analyzed, and more particularly to a reflectance spectroscope and method for determination of non-hemolyzed levels of occult blood in urine.
It is useful for various medical diagnostic purposes to utilize a reflectance spectroscope to analyze samples of body fluid, for example, to detect the presence of blood in a person's urine. Conventional reflectance spectroscopes have been used to detect the presence of blood in a urine sample disposed on a reagent pad. Any blood present in the urine reacts with the reagent on the reagent pad, causing the reagent pad to change color over time to an extent which depends on the concentration of the blood. For example, in the presence of a relatively large concentration of blood, such a reagent pad may change in color from yellow to dark green.
One prior art reflectance spectroscope detects the concentration of the blood by illuminating a single portion of the reagent pad and detecting, via a conventional reflectance detector, the amount of light received from the reagent pad, which is related to the color of the reagent pad. Based upon the magnitude of the reflectance signal generated by the reflectance detector, the spectroscope assigns the urine sample to one of a number of categories, e.g. a first category corresponding to no blood, a second category corresponding to a small blood concentration, a third category corresponding to a medium blood concentration, and a fourth category corresponding to a large blood concentration.
The assignment of a urine sample into one of the categories described above has been performed by successively comparing the magnitude of the reflectance signal with each of three threshold levels which define the categories. For example, if the reflectance signal has a magnitude that corresponds to a 10% light reflectance (which would correspond to a dark reagent pad having a large blood concentration), the spectroscope would compare that 10% reflectance signal with the threshold for large blood concentrations, e.g. 15%, and would assign the urine sample to that category.
One disadvantage of such a conventional spectroscope is the possibility of miscategorizing the blood concentration in cases where non-hemolyzed blood is present. Blood present in a normal urine sample is hemolyzed, which means that the blood is relatively uniformly distributed throughout the urine sample as small blood cell fragments which are visually undetectable. In certain cases, such as in highly concentrated urine, the blood is non-hemolyzed, meaning that there are substantially intact red blood cells or relatively large blood cell fragments present which can be visually detected with the unaided eye or with a small amount of magnification.
When a relatively small amount of non-hemolyzed blood is present in a urine sample, a conventional spectroscope may generate a false negative (erroneously reporting the absence of blood) if the concentration of the individual blood cells is small enough. However, if that same urine sample on the reagent pad were visually inspected by a doctor, the large blood cell fragments could be seen, thus leading the doctor to erroneously believe that the spectroscope was faulty.